First, he says, fertile[521] soils yield a produce that more than feeds the producer. This may be put more generally than Malthus has put it. If rent is to be paid, there must be wherewithal to pay it; and there cannot be so if production does no more than repay cost. There may, however, be a production beyond mere repayment of cost, not only in farming but in all trades. The very principle of the division of labour and the separation of trades implies that devotion to one occupation makes men so dexterous in production that, besides providing for themselves, they have an overplus wherewith to supply their other wants and the wants of others.[522] This overplus, where the facilities for trading were specially good, might be so much above the overplus of an ordinary profit that the granter of the facilities, who is usually the ground landlord, might get the lion’s share of it, and still leave the user of the facilities as thriving as his neighbours. On the other hand, if no such overplus can be earned, no such rent can be paid. Rent, in short, when it is paid by men of business, either in town or in country, means over-profits, and ground-rents mean advantage of situation. The second cause of rent, according to Malthus, who is considering, be it remembered, the cause of the Progress of rents as well as of their actual volume at any given time,[523] is the peculiarity belonging to agricultural land, that the demand increases with the supply; in other cases the demand is external to the supply, but in this case[524] the supply creates its demand. Where there is food there will be mouths. In the supply of food no over-production is possible.[525]